The many systems and parameters which must be monitored during the flight of an aircraft, require a cockpit to be crowded. Some of the most important indicators are located in the cockpit on the instrument panel located where a pilot can easily view the indicators on a continuous base. Each instrument typically monitors one information value. These many indicators are necessary in order to allow monitoring, by a pilot, of the various engine parameters and the environment of the aircraft. However, the large number of such indicators necessitates a very large instrument panel, making the cockpit area confusing and hard to wire.
U.S. Pat. No. 4,575,803 teaches a microprocessor controlled, single display engine monitor and recorder which generates excessive temperature alarms, stores the length of time over predetermined temperatures, and indicates total engine hours. U.S. Pat. No. 3,593,012 teaches an engine life recorder system which generates excessive temperature alarms, excessive speed alarms, and also integrates the speed and temperature signals to generate an engine life cycle value. This recorder system also displays total engine running time. However, according to this patent, each of these displays requires a separate display face. U.S. Pat. 3,250,901 also teaches integration of temperature and engine rotation speed characteristics.
However, all of these patents are relatively disadvantageous because they only display a relatively small number of different functions. Furthermore, since each instrument typically receives only a single input parameter, monitoring of peaks, limits, and percents of temperature can only be roughly estimated. This is because different reference levels are applicable for different operating conditions of the aircraft engine. For instance, when an engine first starts up, it will be normal for the engine to operate hotter than it will operate during normal operation. Therefore, an over-temperature alarm should occur at a different level during starting than it should occur during operating of the engine. Similarly, if total time above a danger temperature is to be recorded, this danger level should be changed based on whether the engine is starting or operating.
According to the present invention, this is advantageously effected by monitoring parameters related to both rotational speed and temperature of the aircraft engine. The rotational speed can be detected to determine if the engine is in start or operate condition. The temperature can then be compared with a threshold that varies based on whether the engine is starting or operating.
None of the prior art has an indicator with a single display that displays values relating to both temperature and rotational speed of the aircraft engine. U.S. Pat. Nos. 3,250,901 and 3,593,012 do monitor both rotational speed and temperature in the same indicator assembly. However, '901 only displays engine life cycle, and '012 displays different parameters on different monitors. Since different monitors are used, extra space on the indicator array is necessary. Furthermore, neither of these patents teach using the rotational speed to determine a starting or operation state, and to choose a reference, based on rotational speed, with which temperature will be compared.
Furthermore, none of these meters enables a plurality of functions as complex as those according to this invention, to be monitored using a single meter. These plurality of functions as monitored by the present invention include peak temperature, length of time over a predetermined temperature, excessive temperature, peaks over a temperature limit for both engine starting and operation modes, peak speed, length of time over a predetermined speed, total engine hours, and engine life cycle. Furthermore, none of these patents enable all the associated circuitry to be in a container having a cross sectional area smaller than the area of the display itself.